Color filters and the methods used to manufacture color filters are known. Color filter producing methods include techniques that deposit color filter material onto a prepatterned substrate. These techniques include, for example, vapor deposition, spin-coating, and thermal deposition (see, for example, U.S. Pat. No. 5,874,188, issued to Roberts et al., on Feb. 23, 1999).
Other methods of manufacturing color filters involve evaporating the color filter material, using heat or ion bombardment, and then depositing the evaporated color filter material onto a substrate using a condensation process or a chemical reaction. In these manufacturing processes, the color filter material must to be thermally stable or have a thermally stable precursor that generates the color filter material on the substrate (when a chemical reaction process is used). As is known in the art, these processes are not adapted to generate patterned layers of thermally unstable color filter materials.
Typically, color filters are formed as a continuous film or and array of pixels. They can include a single color material or multiple color materials (for example, combinations of red, green, and blue; or cyan, magenta, yellow, and black). When multiple color materials are used, the color filter is typically formed using pixels in a two dimensional array. Conventional color filter materials are typically composed of organic and organometallic pigments, semiconductors, ceramics, and combinations thereof.
Inkjet printing systems are commonly used to create high-resolution patterns on a substrate. In a typical inkjet printing system, ink droplets are ejected from a nozzle towards a recording element or medium to produce an image on the medium.
When used to create a color filter, the ink composition, or recording liquid, ejected by the inkjet printing system comprises a color filter material, such as a dye or pigment or polymer, and a large amount of solvent, or carrier liquid. Typically, the solvent is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof. The ink composition usually includes additives designed to preserve pixel integrity after the droplet is deposited on the recording element, or substrate, due to the high concentrations of solvents in conventional color filter ink formulations. Additive materials may include surfactants, humectants, biocides, rheology modifiers, sequestrants, pH adjusters, and penetrants, etc.
U.S. Pat. No. 6,245,393 B1, issued to Thompson et al., on Jun. 12, 2001, discloses a method of making a multicolor display device. The device includes a transparent substrate and a fluorescent dye deposited in a dye layer on the substrate using inkjet printing. This method is disadvantaged because the ink compositions, which include the color filter material, have high solvent concentrations which enables the ejection of the ink composition using conventional inkjet printers. As such, processing steps devoted to the removal of the solvent(s) are required. Additionally, the color filter materials used will not always dissolve or solubilize in commonly available solvents. This can necessitate the use of exotic solvents that are environmentally harmful and/or expensive.
Technologies that use supercritical fluid solvents to create thin films are also known. For example, R. D. Smith in U.S. Pat. No. 4,734,227, discloses a method of depositing solid films or creating fine powders through the dissolution of a solid material into a supercritical fluid solution and then rapidly expanding the solution to create particles of the marking material in the form of fine powders or long thin fibers, which may be used to make films. There is a problem with this method in that the free-jet expansion of the supercritical fluid solution results in a non-collimated/defocused spray that cannot be used to create high resolution patterns on a receiver. Furthermore, Smith does not teach the use of a mask to create high resolution patterns on a receiver.
Other technologies that deposit a material onto a receiver using gaseous propellants are known. For example, Peeters et al., in U.S. Pat. No. 6,116,718, discloses a print head for use in a marking apparatus in which a propellant gas is passed through a channel, the marking material is introduced controllably into the propellant stream to form a ballistic aerosol for propelling non-colloidal, solid or semi-solid particulate or a liquid, toward a receiver with sufficient kinetic energy to fuse the marking material to the receiver. There is a problem with this technology in that the marking material and propellant stream are two different entities and the propellant is used to impart kinetic energy to the marking material. When the marking material is added into the propellant stream in the channel, a non-colloidal ballistic aerosol is formed prior to exiting the print head. This non-colloidal ballistic aerosol, which is a combination of the marking material and the propellant, is not thermodynamically stable/metastable. As such, the marking material is prone to settling in the propellant stream which, in turn, can cause marking material agglomeration, leading to discharge device obstruction and poor control over marking material deposition.
Huck et al., in WO 02/45868 A2, disclose a method of creating a pattern on a surface of a wafer using compressed carbon dioxide. The method includes dissolving or suspending a material in a solvent phase containing compressed carbon dioxide, and depositing the solution or suspension onto the surface of the wafer, the evaporation of the solvent phase leaving a patterned deposit of the material. The wafer is prepatterned using lithography to provide the wafer with hydrophilic and hydrophobic areas. After deposition of the solution (or suspension) onto the wafer surface followed by the evaporation of the solvent phase, the material (a polymer) sticks to one of the hydrophobic and hydrophilic areas. The solution (or suspension) is deposited on the wafer surface either in the form of liquid drops or a feathered spray.
This method is disadvantaged because deposition using a feathered spray requires that the wafer surface be prepatterned prior to deposition. Hence, direct patterning of the wafer surface is not possible because of the diverging profile (feathered) of the spray. Additionally, a wafer surface that has not been prepatterned cannot be patterned using this method. This method also requires time for drying so that the solvent phase of the liquid drops (or feathered spray) can evaporate. During the time associated with solvent phase evaporation, the solvent and the material can diffuse (for example, into the surface or along the surface) degrading the desired pattern
Further, those skilled in the art will appreciate that it is common to use a mask technique for patterned deposition. Typically, the mask employed for patterning on a planar substrate surface is a photoresist material. However, when the surface is nonplanar, difficulties can be encountered in depositing and cleaning off the photoresist material, necessitating the use of shadow masks or stencils. For example, U.S. Pat. No. 4,218,532 titled “Photolithographic Technique For Depositing Thin Films,” issued Aug. 19, 1980 to Dunkleberger discloses a method for patterned deposition of thin films of metals, such as lead alloys, by vacuum evaporation onto a substrate through openings in a mask fabricated with a predetermined pattern. A shortcoming of this development is that it cannot be used for the patterned deposition of thermally unstable color filter materials since these are not suitable for vacuum evaporation.
In U.S. Pat. No. 4,013,502 titled “Stencil Process For High Resolution Pattern Replication,” issued Mar. 22, 1977 to Staples, a process for obtaining high-resolution pattern replication using stencils is disclosed. The stencil in Staples is a mask effecting molecular beam deposition of thin films onto a substrate through openings in the stencil. In this deposition process, the molecular beam source is an electron-beam evaporator. Much like the Dunkleberger development, a shortcoming of Staples' technology is that it cannot be used for patterned deposition of thermally unstable materials that are not suitable for evaporation using an electron beam evaporator.
Furthermore, it is well known that patterned deposition of thermally unstable materials on substrates may be achieved by liquid phase processes such as electroplating, electrophoresis, sedimentation, or spin coating but these processes are system specific. For example, in the case of electroplating, it is necessary that an electrochemically active solution of the functional material precursor is available. In the case of sedimentation and spin coating, a stable colloidal dispersion is necessary. In the case of electrophoresis, it is also necessary that the stable colloidal dispersion be charged. Microfabrication of multi-layer structures usually requires multiple stages, necessitating the complete removal of residual liquids/solvents at the end of every stage, which can be very energy, time, and cost intensive. Further, many of these liquid-based processes require the use of non-aqueous liquids/solvents, which are hazardous to health and the disposal of which can be prohibitively expensive. For example, in U.S. Pat. No. 5,545,307 titled “Process For Patterned Electroplating,” issued Aug. 13, 1996 to Doss et al., a process is disclosed for patterned electroplating of metals onto a substrate 14 through a mask. The Doss et al. process, however, has at least two major shortcomings. First, it is only applicable to materials that have electrochemically active precursors. Second, it uses an aqueous electroplating bath for the process that requires the coated substrate be cleaned and then dried at the end of the coating process.
Moreover, it is well known that to eliminate the need for potentially harmful solvents that need drying, it is possible to use environmental and health-benign supercritical fluids such as carbon dioxide as solvents. For example, in U.S. Pat. No. 4,737,384 titled “Deposition Of Thin Films Using Supercritical Fluids,” issued Apr. 12, 1988 to Murthy et al., a process is disclosed for depositing thin films of materials that are soluble in supercritical fluids onto a substrate. Murthy et al. include the steps of exposing a substrate at supercritical temperatures and pressures to a solution comprising a metal or polymer dissolved in water or a non-polar organic solvent. The metal or polymer is substantially insoluble in the solvent under sub-critical conditions and is substantially soluble in the solvent under supercritical conditions. Reducing the pressure alone, or temperature and pressure together, to sub-critical values cause the deposition of a thin coating of the metal or polymer onto the substrate. Nonetheless, a shortcoming of the process of Murthy et al. is its limited applicability to materials that can be dissolved in compressed fluids, severely limiting the choice of materials that can be deposited on a substrate using this technology. Another shortcoming of the process of Murthy et al. is that it does not teach a process for the patterned deposition of functional materials.
In U.S. Pat. No. 4,582,731 titled “Supercritical Fluid Molecular Spray Film Deposition and Powder Formation,” issued Apr. 15, 1986 to Smith, and U.S. Pat. No. 4,734,227 titled “Method Of Making Supercritical Fluid Molecular Spray Films, Powder And Fibers,” issued Mar. 29, 1988 to Smith, independent processes are disclosed for producing solid films on a substrate by dissolving a solid material into supercritical fluid solution at an elevated pressure. In both cases, the supercritical fluid solution is then rapidly expanded in a region of relatively low pressure through a heated nozzle having a relatively short orifice. Both of the aforementioned Smith processes have similar shortcomings to those indicated above, i.e., they are only applicable to materials that are soluble in compressed fluids and do not teach a process for patterned deposition. There is another problem with this method in that the free-jet expansion of the supercritical fluid solution results in a non-collimated/defocused spray that cannot be used to create high-resolution patterns directly on a receiver. Further, defocusing leads to losses of the marking material
Therefore, a need persists in the art for a patterned deposition method for creating a color filter that permits the patterned deposition of thermally unstable/labile color filter materials and that reduces or eliminates the use of expensive and both environmentally and human health-hazardous solvents. A further need exists for a patterned deposition method for creating color filter that eliminates the need for post-deposition drying for solvent-elimination. Moreover, there is an additional need for a patterned deposition technique that is applicable for a wide range of color filter materials and that is not limited by specific properties of the color filter materials.